C300: C300 with MixPre-D theory question

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Dave Yoder

New member
I'm trying to figure out the best settings for using the MixPre-D with my C300. As I understand it, what I should be doing with my shotgun is sending it into the MixPreD via 48v phantom (of course) and the output to camera should be line level. I then use the tone to set the camera audio to just under -20 so the MixPre D's limiters will kick in before clipping in the camera. That's fine, but I notice that if I set the out to mic level into the camera (and mic level setting on camera), I can turn down the camera audio further, but a couple notches. My question--wouldn't this be better, as presumably it's reducing the use of the in-camera preamps, which are surely inferior to those in the MixPre-D?

As I understand it, the C300's preamps are not bypassed when line level is activated, the signal is still routed through the preamps. I would simply test it myself but my environment is too noisy to do so, I fear, so I resort to theory. Anyone have any thoughts?

Thanks

dave
 
Thanks Ben,

so should I presume the on-camera level dials of the C300 are adjusting completely different signal levels when switched between mic and line? Otherwise what I'm seeing seems to suggest mic level is the stronger signal. I have to dial it down further on camera.

thanks
 
Don't understand the question.

Are you just concerned that the physical dials point differently when calibrated with their respective line-up tones?

I wouldn't be too concerned by variations on the physical dials. They're just variable resistors. Use good quality headphones to monitor and check your output signal matches up with your input (ie line to line or mic to mic.)

Test it and listen carefully to the recorded signal.
 
I have tested the C300 and C100, and I am quite certain that you should just set the camera to auto if you the input is set to line level and you have an actual line level input. I'm almost positive that "auto" just sets the gain staging to proper line level rather than implementing auto gain control as it does for mic level.
 
cpreston said:
I have tested the C300 and C100, and I am quite certain that you should just set the camera to auto if you the input is set to line level and you have an actual line level input. I'm almost positive that "auto" just sets the gain staging to proper line level rather than implementing auto gain control as it does for mic level.
Click to expand...

I would never recommend anyone set a camera to AUTO if you're controlling the audio and feeding it from a mixer. Unless you have some sort of documented, definitive proof that the camera isn't using auto gain when AUTO is activated while in LINE level, you're basically gonna be fighting yourself and defeating the purpose of having someone there with a mixer to control the levels.
 
Run&Gun said:
I would never recommend anyone set a camera to AUTO if you're controlling the audio and feeding it from a mixer. Unless you have some sort of documented, definitive proof that the camera isn't using auto gain when AUTO is activated while in LINE level, you're basically gonna be fighting yourself and defeating the purpose of having someone there with a mixer to control the levels.
Click to expand...
+1
Also, he should rely more on the MixPreD limiters than auto on cam.
 
The manual is junk when it comes to understanding what is going on with the audio on that camera. Based on my testing, it also appears that a setting of 5 or halfway up the dial is actually the 0 gain setting. If you have to lower the gain below 5 in order to keep the sound from clipping on an external mic, you will just end up overloading the input and distorting the signal. Never use a setting below 5 on an external source. At least that is what I've found on the C100. It doesn't say anything about that in the manual.

The manual also says to set the peaks to -20dB and yet the AGC tries to maintain -10dB and generally has a trouble keeping things from clipping.

Anybody have any idea of the built in limiter is pre or post A/D?

By the way, I was wrong about the auto setting on line level. It does implement the AGC. It just does it in a weird way. It only really kicks in when the signal gets above -10dB.
 
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In my C300, I normally max the audio gain dial setting beyond 5 ie. the half way mark and rarely at 6 as there is increase in noise beyond that. 5 is what I am comfortable at. When the sound is loud and microphone is closer, I am close to 3. Below 3 the signal becomes pretty weak.

If you are using a Mix Pre D, then I would recommend that you use the gain in Mixpre D higher and the dial setting in the C300 to as low as possible to get the right levels in the camera. The MixPre D has digital outputs, so the quality would be better.

I never ever use the AGC. In face one should never use it. In 2012, when I first got a demo camera from Canon for testing, one reputed filmmaker had just returned the demo unit. I didn't notice that AGC was on. And my first few shots were ruined. Fortunately, I played back and tested immediately to know that AGC was on. When you are interviewing a person in the outdoors, the moment there is a pause between his words, the AGC pushes up the ambient noise level. So suddenly you hear the distant bird tweeting and the sound of the leaves swaying in the gentle breeze goes up. This just ruins the recording. So absolutely no AGC at all.

How are you mounting the MixPre D?
 
If you are using a mixer with a camera, use line level.

You don't actually want to run the mic level below 5 in order to reduce a hot signal as you run the risk of overloading and distorting the preamp. If you setting the levels much below 5 on mic level, you should be setting a pad or lowering the trim in the audio menu.
 
Does the mix-pre not output 1k tone to set camera levels like a "real mixer"? I run everything at line level and SOP is send tone to the cam, set the levels on the camera at "zero"(-20) and lock them down. From then on out, all levels are adjusted from the mixer.
 
Thanks everyone,

So... It sounds like perhaps I'm doing the right thing:

I set input +48v into the MixpreD and line level out to the camera (which is set at line). then using the MixPreD tone I drop the on-camera dial until it's just under -20db, and make sure the MixPre limiters are on. In my rough tests, I don't seem to see any clipping on-camera when I push them and the MixPreD limiters activate. The SD limiters are supposed to be really good, and the SD manual says it doesn't affect sound at all before clipping, so... is that optimal? The on-camera dial is I think at 5 in this scenario. And I wouldn't get any benefit from dropping the camera gain because then to compensate I'd just be activating the MixPreD limiters and wouldn't be getting the levels I want (and would be adding whatever the SD limiters do to it). Please enlighten me if I'm wrong!

Next... wireless lavs. Oh joy. The things actually intimidate me, I've yet to be able to place them hidden without it sounding like a gravel truck.
 
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